Diffusion-transfer reversal process



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Patented July 3, 19%2 This invention relates to a novel photographicprocess. More particularly, this invention relates to a novel ditfusion-transfer reversal process wherein ordinary tap water is used as theprocessing liquid.

The diffusion-transfer reversal process, referred to hereinafter as theDTR process, comprises exposing a photographic element comprising a basehaving thereon a coating of a light sensitive silver halide emulsion anddeveloping the exposed coating with a developer containing a silverhalide solvent while the coating is in contact with a specially-preparedlayer which is not light sensitive. In the course of forming a negativeimage in the exposed coating, the solvent in the developer dissolves theunexposed silver halide which is transferred image-wise to thespecally-prepared layer toform thereon a positive image by reaction ofthe dissolved silver-halide with substances present in the layer. TheDTR process as heretofore practiced is relatively slow, complicated anddiflicult to control.

It is an object of this invention to provide a novel diffusion-transferreversal process which is simple and materially easier and faster inoperation than the known DTR processes.

It is a further object of this invention to provide a noveldiffusion-transfer process utilizing a commercial print-out emulsion asthe photosensitive layer.

It is a still further object of this invention to provide a noveldiffusion-transfer process utilizing water for accomplishing thetransfer of the image from the photosensitive layer to the receivinglayer.

Other objects and advantages of this invention will appear to thoseskilled in the art from the detailed description thereof given below.

Briefly, the novel process of this invention comprises exposing aphotosensitive film comprising a base having as a photosenistive layer aknown print-out emulsion and then pressing the exposed film against animage receiving layer in the presence of moisture. The moisture may besupplied by means of ordinary tap water or deionized water. The pressingof the two layers may take place at room temperature. A contact time offrom 120 seconds, preferably about 2 to 5 seconds is sufficient toaccomplish the transfer of the image. The two very slightly moist layersare then separated and dried.

If desired, this process can be practiced as a dry process. Heat alonemay be utilized to accomplish the transfer of the image. A reagent canbe added to the coating which loses moisture on heating. Such reagent isdisclosed in German Patent No. 888,045 and in Bild und T011, 11, 62(1958). The increased temperature may be such as to speed up thediffusion to such an extent that a more rolling of the contacting layersbetween hot rollers will be sufficient to transfer the image.

If desired, this process can be practiced as a semi-dry process. Themoisture necessary to accomplish the transfer may be supplied in theform of steam. These last named modifications would, for all practicalpurposes, be dry transfer processes.

Print-out emulsions are well known in the art. These emulsions aredescribed in various publications. Special reference is here made topages 245-257 of a book by T. T. Baker entitled, Photographic EmulsionTechnique 1948, published by American Photographic Publishing Company.These emulsions are also described in a book entitled, PhotographicFacts and Formulas (1947), pages 188200, by E. 1. Wall and in a bookentitled, Chimie Photographique (1957), pages 299401, by PierreGlafkides.

An example of a print-out emulsion composition which is given in thebook by Baker is the following:

Ammonium chloride g 2.5 Sodium potassium tartrate g 5.0 Gelatin g 80.0Silver nitrate g 25 .0 Citric acid g 10.0 Water cc 1000.0 Alcohol -cc-400 Many variations in both the ingredients and proportions of print-outemulsions are described in the various books referred to above. Theseemulsions all contain a soluble silver salt such as silver nitrate, forexample, a halide, such as ammonium chloride, sodium chloride, etc,capable of reacting with the soluble silver salt to form silver halide,the amount of soluble silver salt in the composition being in excess ofthat which will react with the halide to form silver halide so that acertain amount of the soluble silver salt is present in the emulsionafter exposure. In addition to the aforesaid essential components, suchemulsions may also contain various secondary adjuncts such assurfactants, ultraviolet absorbers and the like.

The print-out emulsion may be coated on any desired base used in thephotographic art. Among the suitable bases are the cellulose esters suchas cellulose acetate, cellulose nitrate, for example, the vinyl resinssuch as vinyl acetate, paper, metals and others.

The image-receiving layer may be baryta subbed paper base as such or thebaryta paper may be coated with a layer containing any one or a mixtureof the following substances: ZnO, Mn(OAc) ZnO+Mn(OAc) TiO TiO =+Mn(OAc)ascorbic acid, colloidal ZnS, coll. CdS, colloidal Ag, colloidal sulfur,Na S, Z-mercaptobenzothia- Zole, phenyl-mercapto-tetrazole, colloidalsilica such as silica aerogel, Santogel, fullers earth, diatomaceousearth, kieselguhr, wood flour, infusorial earth, bentonite, filter aidssuch as Celite, Super-Floss and finely-powdered glass, talc, mica andthe like.

Upon exposure of the light sensitive layer, photolytic silver is formedin the exposed areas. This photolytic silver does not diffuse. Theunexposed areas contain still the soluble silver salts such as silvernitrate, silver citrate and/or silver and ammonia complexes, dependingupon the composition of the print-out type emulsion used. Upon contactof the exposed layer with the image receiving layer in the presence ofwater, the water soluble silver salts dissolve and diffuse into theimage-receiving layer to form the image.

The difierences between the prior art DTR processes and the novel DTRprocess of this invention may be summarized as follows:

In the prior art processes, only silver halide is used in the lightsensitive emulsion. I use soluble silver salts in my light sensitiveemulsion. The prior art processes use a viscous, complicated, unstablepaste which must be applied uniformly to form a film of uniformthickness in order to properly develop and transfer the image. I useonly water, which may be ordinary tap water, for this purpose. The priorart process must include a solvent for silver halide in the processingpaste. I do not use any silver halide solvent. In fact, I do not needany silver halide at all. It may, sometimes, be desirable to have somesilver halides present in the light sensitive layer in order to increasespeed or to extend the spectral sensitivity of this layer by optical orchemical sensitization. However, the silver halide is no essentialingredient and does not take part in the DTR step. The development andtransfer of the prior art processes takes about 60 seconds whereas in myprocess 3 seconds or less is sufficient. My process may be carried outin the presence of room light whereas the prior art processes must becarried out in darkness.

The following specific examples illustrate my novel process. It is to beunderstood, however, that these examples are given by of illustrationand not by way of limitation.

Example I (1) A light sensitive coating was prepared by adding to acommercial print-out emulsion as obtained from production (50.0 g.) a20% aqueous formaldehyde solution (1.0 ml.), and coating the abovemixture at 40 C. onto a subbed cellulose triacetate film base.

(2) The light sensitive coating was exposed for 5 minutes as follows:

The coating was placed behind a photographic negative in a printingframe. The printing frame was placed 41 cm. from a Medium Beam ReflectorPhoto Lamp. Be-

tween the lamp and the printing frame was placed an 18 cm. wide,parallel-sided battery jar filled with deionized water. The lightintensity at the plane, where the printing frame stood during exposure,was set at 200 footcandles. The intensity of the lamp output wascontrolled by means of a voltage regulator. The light intensity wasmeasured before each exposure with a Weston Foot-Candle Meter, modelL-61.

(3) The exposed light sensitive coating was rolled into contact with theimage-receiving paper which consisted of baryta subbed paper basethrough a bath containing tap water for a period of 5 seconds.

The coatings were then stripped apart 5 seconds after they had emergedtogether from the roller system.

(4) The image on the image-receiving paper was then washed for 1 minutewith running (20 C.) tap water.

It was found that:

(1) Both the exposed and unexposed areas of the light sensitive coatingtransferred to the image-receiving paper base.

(2) When washed with cold water, the unexposed background (Ag washedalmost entirely off, but the exposed letters (Ag") did not. Thus, apositive image consisting of dark brown-black letters on a pinkbackground was obtained.

Example II (1) The light sensitive coating was prepared by coating thefollowing mixture (40 C.) on baryta subbed paper base: Commercialprint-out emulsion g 50 MnSO .4l-I O (50% aqueous solution) m1 1 (2) Theimage-receiving coating was prepared by coating the following mixture(40 C.) on baryta subbed paper base:

% aq. surface gel 'g 35 8% aq. Saponin .ml 0.5 Standard Agl emulsion g 510% aq. formaldehyde e ml '0.5

(3)The light sensitive coating was exposed through a photographicpositive for 5 minutes in the same setup as described in Example I, step2. V

(4) The exposedlight sensitive coating was rolled into contact with theimage-receiving coating through a bath containing deionized water for aperiod of 5 seconds.

The coatings were then stripped apart 5 seconds after they had emergedtogether from the roller system.

The image-receiving layer was then dipped into 5% aqueous NaOH for 30seconds, and then washed 1 minute with runnin 20 C. tap water.

It was found that:

(1) Almost all of the unexposed and part of the exposed portions of thelight sensitive coating transferred to the image-receiving layer.

(2) A reversal image consisting of dark brown letters on a darkbackground was obtained.

Example 111 (l) The light sensitive coating was prepared by coating thefollowing mixture (40 C.) on transparent film base:

Commercial print-out emulsion g 15 Standard silver chloride emulsion g35 8% aq. Saponin ml 0.3 10% aq. solution of K-Cr-Alum ml 1 (1) Theunexposed letters transferred very nicely from the exposed to theimage-receiving layer; very little of the exposed background transferredto the image-receiving layer.

(2) An acceptable positive image consisting of lightblack letters on anoff-white background was obtained.

(3) No washing of the receiving layer is necessary.

Example IV (1) The light sensitive coating used was the same as thatdescribed in Example III, step 1.

(2) The image-receiving coating was prepared by pulling strips of barytasubbed paper base through a solution consisting of 30 mg. of2-mercaptobenzothiazole per liter of distilled methanol; these stripswere dried thoroughly before using.

(3) The light sensitive coating was exposed through a photographicpositive for 6 minutes in the same setup as described in Example I, step2.

(4) The exposed light sensitive coating was rolled into contact with theimage-receiving coating through a bath containing tap water for a periodof 5 seconds.

The coatings were then stripped apart 5 to 10 seconds after they hademerged together from the bath.

It was found that:

(1) The unexposed letters of the light sensitive coating transferredsatisfactorily to the image-receiving layers; very little of the exposedbackground transferred.

(2) A reversal image consisting of red-brown letters on a light-pinkbackground was obtained.

Example V (1) The light sensitive coating used was the same as thatdescribed in Example III, step 1.

(2) The image-receiving coating was prepared by pulling strips of barytasubbed paper base through a solution consisting of 30 mg. ofphenyl-mercapto-tetrazole per liter of distilled methanol; these stripswere dried thoroughly before using.

(3) The light sensitive coating was exposed through a photographicpositive for 6 minutes in the same setup as described in Example I, step2.

(4) The exposed light sensitive coating was rolled into contact with theimage-receiving coating through a bath containing tap water for a periodof 5 seconds.

The coatings were then stripped apart 5 to 10 seconds after they hademerged together from the roller system.

5 It was found that:

(1) The unexposed letters of the light sensitive coating transferredsatisfactorily to the image-receiving layer; very little of the exposedbackground transferred.

(2) A reversal image consisting of red-brown letters on a verylight-pink background was obtained.

Example VI (1) The light sensitive coating was the same as in ExampleIII, step 1.

(2) The image-receiving layer was prepared by coating the followingmixture (40 C.) on baryta subbed paper base:

8% surface l ag 49 8% aq. Sapom'n ml 0.5 ZnO g 1.0 Mn(OAc) solution (9g./ 100 ml. H O) ml 2.0

(3) The light sensitive coating was exposed through a photographicpositive for 5 minutes in the setup described in Example I, step 2.

(4) The exposed light sensitive coating was rolled into contact with theimagereceiving coating through a bath containing deionized water for aperiod of 5 seconds.

The coatings were then stripped apart to 20 seconds after they hademerged together from the roller system.

It was found that:

Example VII (1) The light sensitive layer used was the same as thatdescribed in Example III, step 1.

(2) The image-receiving layer was prepared by coating the followingmixture (40 C.) on baryta subbed paper base:

8% surface gel g 49 g 1 8% Saponin ml 0.5 Mn(OAc) solution (9* g./10Oml. H O) ml v 2 (3) The light sensitive coating was exposed through aphotographic positive for minutes in the same setup as described inExample I, step 2.

(4) The exposed light sensitive coating was rolled into contact with theimage-receiving coating through a bath containing tap water for a periodof seconds.

The coatings were then stripped apart 0 to 20 seconds after they hademerged together from the roller system.

It was found that:

(l) The unexposed letters of the light sensitive layer transferredsatisfactorily to 'the image-receiving coating. The exposed backgroundtransferred very little to the image-receiving coating.

(2) A reversal image consisting of red-brown letters on a pinkishbackground was obtained.

Example VIII (1) The light sensitive coating used is the same as thatdescribed in Example III, step 1.

(2) The image-receiving layer consisted of colloidal 6 zinc sulfide ingelatin (see U.S.P. 2,843,485, Yutzy and Cowden, Example I) prepared inthe following manner:

(a) Solution A: 1 g. Na S in 1000 ml. deionized H O. Solution B: 1 g.Zn(NO .611 0 in 1000 m1. deionized H20- (b) With rapid stirring, ml. ofsolution B was poured into a solution consisting of 23 m1. of solution Adiluted with 157 cc. of deionized H 0.

(0) The above mixture was poured quickly (at 40 C.) into a solution ofgrams of 20% gelatin containing 10 cc. of 7.5% aqueous Saponin at 40 C.

(d) The mixture was held at 40 C. for 15 minutes, then coated at 40 C.on baryta subbed paper base.

(3) The light sensitive coating was exposed through a photographicpositive for 5 minutes using the setup described in Example I, step 2.

(4) The exposed light sensitive coating was rolled into contact with theimage-receiving coating (which had been dampened with H O) through abath containing tap water for a period of 5 seconds. The coatings werethen stripped apart from 0 to 20 seconds after they had emerged togetherfrom the roller system.

It was found that:

(l) The unexposed letters of the light sensitive coating transferredsatisfactorily to the image-receiving layer; only very small portions ofthe exposed background also transferred to the image-receiving sheet.

(2) A reversal image consisting of very stable, dark brown letters on aslightly pink background was obtained.

Example IX (1) The light sensitive coating used is the same as thatdescribed in Example III, step 1.

(2) The image-receiving layer was prepared by coating the followingmixture (40 C.) on baryta subbed paper base:

20% gelatin solution g 110 Deionized water ml 157 Na S solution (1 g. in1000 ml. deionized H O) ml 23 7.5% aq. Saponin ml 10 (3) The lightsensitive coating was exposed through a (l) The unexposed letters of thelight sensitive coating transferred to the image-receiving layer;extremely small amounts of the unexposed background transferred to theimage-receiving coating.

(2) A reversal image consisting of light-brown and very stable letterson a white background Was obtained.

Example X 1) The light sensitive coating used is the same as thatdescribed in Example III, step 1.

(2) The image-receiving coating was prepare-d by pulling strips ofbaryta subbed paper base through a slurry of 2.0 grams of zinc oxide in200 ml. of deionized waterv (mixing at 60 volts in a metal cup on aWaring Blendor). (3) The light sensitive coating was exposed through aphotographic positive for 5 minutes in the same setup as described inExample I, step 2.

(4) The exposed light sensitive coating was rolled into contact with theimage-receiving layer through a bath containing tap Water for a periodof 2 seconds. The

coatings were stripped apart to 20 seconds after they had emergedtogether from the roller system.

It was found that:

(1) The unexposed letters of the light sensitive coating transferredsatisfactorily to the image-receiving layer; the exposed backgroundtransferred very little to the image-receiving layer.

(2) A versal image consisting of brown letters on an even background wasobtained.

Example X1 (1) The light sensitive coating was the same as thatdescribed in Example III, step 1.

(2) The image-receiving layer was prepared by pulling strips of barytasubbed paper base through a mixture of 2 grams of TiO in 200 ml. ofdeionized water (mixing at 60 volts in a metal cup on a Waring Blendor).

(3) The light sensitive coating was exposed through a photographicpositive in the setup described in Example I, step 2.

(4) The exposed light sensitive coating was rolled into contact with theimage-receiving layer through a bath containing tap water for a periodof 2 seconds.

The coatings were then stripped apart 0 to 20 seconds after they hademerged together from the roller system.

It was found that:

(1) The unexposed letters of the light sensitive coating transferredvery nicely to the image-receiving layer, but little of the exposedbackground transferred to the image-receiving layer. 7

(2) A reversal image consisting of brown letters on a pinkish backgroundwas obtained.

Example XII 1) The light sensitive coating was the same as that used inExample III, step 1.

(2) The image-receiving layer was prepared by coating Lhe followingmixture (40 C.) on baryta subbed paper ase:

Colloidal zinc sulfide (see Example VIII, step 2) ml 50 Ascorbic acid g1 10% aqueous K-Cr-Alum ml 0.5 TiO ..g 0.5

( 1) The unexposed letters of the light sensitive layer transferredsatisfactorily to the image-receiving layer; none of the exposedbackground transferred.

(2) A reversal image consisting of brown stable letters on a whitebackground was obtained.

Example XIII (1) The light sensitive layer was the same as thatdescribed in Example III, step 1.

(2) The image-receiving layer was prepared by pulling strips of barytasubbed paper base through a solution consisting of Silica powder(Floated Powder, 240 mesh, Fisher,

Catalog No. S153) g 0.5 Deionized water ml 100 Ascorbic acid g 1.0

(3) The light sensitive layer was exposed through a photographicpositive for 4 minutes in the setup described in Example I, step 2.

8 (4) The exposed light sensitive coating was rolled into contact withthe image-receiving coating through a bath containing tap water for aperiod of 10 seconds.

The coatings were then stripped apart 5 seconds after they had emergedtogether from the roller system.

It was found that:

('1) The unexposed letters of the light sensitive layer transferred tothe image-receiving layer; the exposed background did not transfer.

(2) A reversal image consisting of brown-black letters on a whitebackground was obtained.

Example XIV (1) The light sensitive layer was the same asin Example III,step 1.

(2) The image-receiving layer was prepared by pulling strips of barytasubbed paper base through a mix- .ture of 0.1% aqueous Zn(NO .6H Osolution ml 100 0.1% aqueous Na S solution ml 23 Deionized water ml 1 57Ascorbic acid g 1.0

Silica (Floated Powder240 Mesh., Fisher, Catalog No. S-153) g 0.5

- (1) The unexposed letters of [the light sensitive coating transferredto the image-receiving layer, the exposed background transferred also alittle to the image-receiving coating.

(2) A reversal image consisting of brown letters on a grey-whitebackground was obtained.

3,3-diethyl-9-methylthiacarbocyanine iodide S S (I CCH=E CH=C l ilt IR(25 mg./25O ml. methanol) ...;ml 0.25 Deionized water ml Ascorbic acid g1.0 Silica (same as Example XIV, step 2) g 0.5

(3) The light sensitive coating was exposed through a photographicpositive for a period of 5 minutes in the setup described in Example I,step 2.

('4) The exposed light sensitive coating was rolled into contact withthe image-receiving coating through a bath containing tap water for aperiod of 2 seconds.

The coatings were stripped apart from 0 to 20 seconds after they hademerged together from the roller system.

It was found that:

(1) The unexposed letters of the light sensitive coating transferred tothe image-receiving coating; some of the exposed background transferredalso.

(2) A reversal image consisting of brown letters on a pink-brownbackground was obtained.

Example XVI 1) The light sensitive coating was the same as thatdescribed in Example IH, step 11.

(2) The image-receiving coating was prepared by coating the followingmixture (at 40 C.) on baryta subbed paper base:

A suspension of colloidal silver in gelatin (with 9 g. of colloidalsilver per kg. of suspension and particle sizes of 20-30 millimicronsdiameters) g 6% surface gel ml 3 5 aqueous K-Cr-Alum ml 1 Ascorbic acidg 1 8% Saponin ml 0.3

(3) The light sensitive layer was exposed through a photographicpositive for 5 minutes in the same setup as described in Example I, step2.

(4) The actual image transfer was made as follows:

The exposed light sensitive coating was rolled into contact with thedampened image-receiving coating through a bath containing tap water fora period of 2 seconds.

The coatings were then stripped apart 5 seconds after they had emergedtogether from the roller system.

It was found that:

(1) The unexposed letters transferred very satisfactorily to theimage-receiving layer; no background transfer took place.

(2) A reversal image consisting of very stable, black letters on yellowbackground was obtained.

Example XVII 1) The light sensitive coating was prepared as follows:

MI. 6% aq. surface gel 40 Aq. AgNO solution A 5 Water 3 Ammonium citratesolution B 1 10% aq. Potassium Chrom Alum 2 8% aq. Saponin 0.5

The above mixture was coated on subbed film base and paper.

(A) 0.850 g. AgNO per 5 ml. volume (B) Mix the following ingredients:

Water ml 50.0 Citric acid g 12.0 28% NH OH m1 12.0

slowly, with stirring and cooling. Ref.: Phot. Eng, 5 127 (1954).

(2) The image-receiving coating was prepared by coating the followingmixture at 40 C. on subbed film base and paper:

Yellow Filter Noodles (same as in Example XVI) g 0.05 6% aq. surface gel-ml 50,0 10% aq. Potassium Chrom Alum mL 1.0 Ascorbic acid g 1.0 8% aq.Saponim ml 0.5

10 (2) An almost completely dry reversal image consisting of verystable, black letters on a light yellowish background was obtained. (3)It was found that the final image can be stored for long periods of timewithout deleterious effects.

The apparatus used in pressing together the light sensitive layer andthe image-receiving layer may be of very simple construction. Thus, oneof the layers may be wetted with water and the two layers pressedtogether by running over them with a rubber roller. The two layers arethen separated and dried. The image appears on the image-receivinglayer. The two layers may also be placed into a Constat or Ozalid PhotoCopy Processor machine. This machine is nothing more than a rubberroller system mounted in a tray. In operation, the tray is cfilled withwater and the handle turned which causes the two rollers to rotate atthe same speed resulting in the two layers being pressed together.

Modifications will appear to persons skilled in the art. I, therefore,do not intend to be limited in the patent granted except as necessitatedby the appended claims.

I claim:

1. A process of forming a positive silver image in an image receivinglayer which comprises imagewise exposing a silver salt print-outemulsion layer containing a water-soluble silver salt so as to formmetallic silver in the exposed areas of said print-out layer and thencontacting said exposed silver salt emulsion layer under pressure withsaid image receiving layer in the presence of pure water, whereby saidwater-soluble silver salt in the unexposed portions of the emulsion isdissolved in said pure water, transferred to the receiving layer andconverted into metallic silver in the presence of a nucleating agent forpromoting image formation which is located in said image receivinglayer, thereby transforming the dissolved silver salt which istransferred and deposited in said receiving layer into a visible image.

2. A process according to claim 1 wherein said nucleating agent is achemical precipitant.

3. A process according to claim 1 wherein said nucleating agent forpromoting image formation comprises physical development nuclei.

4. A process of forming a positive silver image in an image receivinglayer comprising a baryta subbed paper having a coating comprisingphenyl-mercapto-tetrazcle thereon, which comprises exposing imagewise, asilver chloride print-out emulsion layer containing an excess of silvernitrate so as to form metallic silver in the exposed areas of saidprint-out layer and then contacting said exposed silver chlorideprint-out emulsion under pressure with said image receiving layer in thepresence of pure water which is used as the sole processing agent,thereby dissolving the silver nitrate in the unexposed portions of theprint-out emulsion and transferring it to the receiving layers wheresaid dissolved water-soluble silver salt is deposited as metallic silverin visible form.

5. A process as recited in claim 1 wherein the soluble silver salt issilver nitrate.

6. A process as recited in claim 1 wherein the soluble silver salt issilver citrate.

7. A process as recited in claim 1 wherein the printout emulsion alsocontains silver chloride as the silver salt.

8. A process as recited in claim 1 wherein the imagereceiving layercomprises baryta subbed paper.

9. A process as recited in claim 1 wherein the imagereceiving layercomprises baryta subbed paper having a coating thereon comprising MnSO10. A process as recited in claim 1 wherein the imagereceiving layercomprises baryta subbed paper having a coating thereon comprisingascorbic acid.

11. A process as recited in claim 1 wherein the imagereceiving layercomprises baryta subbed paper having a coating thereon comprisingphenyl-mercapto-tetrazole.

12. A process as recited in claim 1 wherein the imagereceiving layercomprises baryta subbed paper having a coating thereon comprising ZnO.

13. A process as recited in claim 1 wherein the imagereceiving layercomprises baryta subbed paper having a coating thereon comprisingMn(OAc) 14. A process as recited in claim 1 wherein the imagereceivinglayer comprises baryta subbed paper having a coating thereon comprisingTiO 15. A process as recited in claim 1 wherein the imagereceiving layercomprises baryta subbed paper having a coating thereon comprising Na S.

16. A process as recited in claim 1 wherein the imagereceiving layercomprises baryta subbed paper having a coating thereon comprising Zn(NO17. A process as recited in claim 1 wherein the imagereceiving layercomprises baryta subbed paper having a coating thereon comprising ZnS.

18. A process as recited in claim 1 wherein the imagereceiving layercomprises baryta subbed paper having a coating thereon comprising Silicain finely dispersed form.

19. A process as recited in claim 1 wherein the imagereceiving layercomprises baryta subbed paper having a coating thereon comprisingcolloidal silver.

20. A process as recited in claim 1 wherein the imagereceiving layercomprises Z-mercaptobenzothiazole.

21. A process as recited in claim 1 wherein the moisture is supplied bymeans of tap water.

22. A process as recited in claim 1 wherein the moisture is supplied bymeans of deionized water.

23. A process as recited in claim 1 wherein the moisture is'supplied bymeans of steam.

References Cited in the file of this patent UNITED STATES PATENTS2,846,309 Land Aug. 5, 1958 FOREIGN PATENTS 566,522 Canada Nov. 25, 1958695,905 Great Britain Aug. 19, 1953 OTHER REFERENCES Dybvig et a1.:Photographic Engineering, vol. 5, No. 2, pp. 127-132 (1954).

1. A PROCESS OF FORMING A POSITIVE SILVER IMAGE IN AN IMAGE RECEIVINGLAYEER WHICH COMPRISES IMAGEWISE EXPOSING A SILVER SALT PRINT-OUTEMULSION LAYER CONTAINING A WATER-SOLUBLE SILVER SALT SO AS TO FORMMETALLIC SILVER IN THE EXPOSED AREAS OF SAID PRINT-OUT LAYER AND THENCONTACTING SAID EXPOSED SILVER SALT EMULSION LAYER UNDER PRESSURE WITHSAID IMAGE RECEIVING LAYER IN THE PRESENCE OF PURE WATER, WHEREBY SAIDWATER-SOLUBLE SILVER SALT IN THE UNEXPOSED PORTIONS OF THE EMULSION ISDISSOLVED IN SAID PURE WATER, TRANSFERRED TO THE RECEIVING LAYER ANDCONVERTED INTO METALLIC SILVER IN THE PRESENCE OF A NUCLEATING AGENT FORPROMOTING IMAGE FORMATION WHICH IS LOCATED IN SAID IMAGE RECEIVINGLAYER, THEREBY TRANSFORMING THE DISSOLVED SILVER SALT WHICH ISTRANSFERRED AND DEPOSITED IN SAID RECEIVING LAYER INTO A VISIBLE IMAGE.